Present day commercial lightwave transmission networks use optical fibers to carry large amounts of multiplexed information over long distances from a transmit terminal to a receive terminal. Most long-haul transmission lines and a substantial portion of short-haul transmission lines such as inter-office and intra-office links, local area networks (LANs), metropolitan area networks (MANs), and wide area network (WANs) are optical and, therefore, the information is carried over an optical fiber. A major advantage of transmitting information in optical form is the very large bandwidth and low losses associated with single mode optical fibers.
To reduce cost while still maintaining an acceptably low blocking characteristic, space-division switching networks are frequently designed to include a plurality of stages of switching nodes. The node stages are successively interconnected using a specified interconnection pattern. To achieve the overall switching function of connecting any network inlet to any network outlet, the individual switching nodes are typically selective in that they can connect any one of a plurality of node inputs to any one of a plurality of node outputs in response to control signals defining the desired connections. A necessary component for selectively interconnecting the nodes of a communication network in this manner, however, is a high capacity matrix or cross-connect switch.
In practice, at the transmitting end of an optical fiber, electrical signals representative of intelligence are transformed into optical signals for transmission along the optical fiber and, at the receiving end, are transformed back into electrical signals for further processing. Furthermore, in today's networks, the optical signals are converted to electrical signals, and back to optical, in order to use electronic switches to switch the various channels to their destinations, and/or to perform electronic regeneration in very long links. More recently, efforts have been made to develop an all optical, strictly non-blocking cross connect structure. In FIG. 1, for example, there is shown an example of a strictly non-blocking, all-optical MN.times.MN cross-connect structure 410 deployed as an intermediate node of an optical network.
As seen in FIG. 1, multiplexed optical signals are supplied from input optical fibers 1 through M. Each optical channel is separated to respective wavelengths .lambda..sub.1 through .lambda..sub.N by a corresponding one of the wavelength demultiplexers. The demultiplexed wavelengths enter the MN.times.MN cross connect structure 410 and are directed, via an optical frequency converter and a wavelength demultiplexer, to appropriate output fibers 1 through M for transmission to a destination node. Although cross-connect structure 410 is non-blocking in that any idle inlet is always connectable to any idle outlet regardless of other array interconnections, the enormous size, design complexity, and large number of intercormections required for such a structure make it extremely expensive to fabricate and thus unsuitable for commercial applications.
It is, however, realized that with an all-optical network where optical signals can flow between users across the network without being converted to electronic signals within the network, the bandwidth available in optical fibers can be accessed in a more flexible and economic way. The benefits and advantages of being able to optically access the very broad bandwidth of optical fibers would permit a high-capacity, high speed network to be established for carrying data or information such as blueprints, words, music, medical and scientific images, movies, E-mail and the like from one location to another.